Nowadays, ceramic materials are widely used in the electronics industry as dielectric resonators, microwave filters, substrates for microelectronic switching circuits, and so on. These components are used in systems for wireless telecommunications, satellite antennas, radar systems, as well as microwave ovens.
The most important properties of the ceramic materials are their relative permittivity ε, the temperature coefficient of their resonant frequency TKf and their quality factor Qxf, which is a measure of the dielectric losses in the material. These properties are of particular importance for use in microwave components. The higher the quality factor, the lower the dielectric losses and the more selectively a microwave component can be tailored to a specific frequency with the aid of the ceramics.
During the course of the continuing miniaturization of ceramic components, especially in frequency ranges up to between 1 and 2 GHz, it is becoming increasingly important to use ceramic materials with high relative permittivity. Such materials permit the production of ceramic components with very small dimensions, such as those that can be used advantageously in wireless telecommunications systems.
A ceramic material is known from printed publication JP 01234358 which is produced on the basis of titanium oxide, barium oxide and neodymium oxide. This ceramic material contains an additive of samarium oxide. The amount of samarium oxide added is used to adjust the temperature response of the resonant frequency of the ceramic material. A ceramic composition for microwave applications is known from printed publication JP 02239150 A, which is produced on the basis of barium oxide, titanium oxide, samarium oxide, cerium oxide and neodymium oxide.
The disadvantage of the ceramic materials specified in the foregoing Japanese documents is that they exhibit a relatively low relative permittivity ε value of between 85 and 90. As a result, highly miniaturized microwave components cannot be produced with these ceramic materials.
A ceramic material is known from the printed publication by A. Kania, “Ag(Nb1-xTax)O3 Solid Solutions—Dielectric Properties and Phase Transitions,” Phase Transitions, 1983, Volume 3, pp. 131 to 140, which is produced on the basis of silver, niobium and tantalum, hereinafter referred to as ANT, and is present in the form of a “solid solution” of the two materials AgNbO3 and AgTaO3. The ceramic material described in this publication exhibits the composition Ag(Nb1-xTax)O3, hereinafter referred to as ANTx, wherein x can vary between 0 and 0.7. Depending on the composition, the ceramic material exhibits an ε of between 80 and 400 at a temperature of approximately 300 K.
It is known, from the printed publication by Matjaz Valant and Danilo Suvorov, “New High-Permittivity Ag(Nb1-xTax)O3 Microwave Ceramics: Part 2, Dielectric Characteristics,” J. Am. Ceram. Soc. 82[1], pp. 88-93 (1999), that disc-shaped ceramic objects comprised of ANT with an x-parameter of between 0.46 and 0.54 exhibit a high relative change in relative permittivity ε in the temperature interval between −20° C. and 120° C. In particular, it was demonstrated at the same time that the progression of the relative change in ε with the temperature follows a curve that exhibits a maximum between 20° C. and 70° C., and assumes values of between −0.07 and 0.01.
It is also known, from printed publication WO 98/03446, that the temperature coefficient of relative permittivity TKε at individual temperatures can be reduced to very small values down to ±70 ppm/K as a result of doping ANT with lithium, wolfram, manganese or bismuth.
Although the known ANT materials exhibit a high ε, they are disadvantageous in that the values of TKε are relatively high in the temperature range that is of interest for applications, i.e., between −20° C. and 80° C.